Suppose x1, x2, . . . , xn are observed values resulting from a random sample from a symmetric but possibly heavy-tailed distribution. Let x

~ and fs denote the sample median and fourth spread, respectively. Chapter 11 of Understanding Robust and Exploratory Data Analysis (see the bibliography in Chapter 6) suggests the following robust 95% CI for the population mean (point of symmetry):

x

~   


fs n



The value of the quantity in parentheses is 2.10 for n
10, 1.94 for n
20, and 1.91 for n
30. Compute this CI for the data of Exercise 45, and compare to the t CI appropriate for a normal population distribution.